Planarian flatworm (freshwater pest) (Girardia tigrina) care guide

Group
Other invertebrates
Other names
Planaria, Brown planarian, Dugesia tigrina, Immigrant flatworm, Planaria tigrina
Family
Dugesiidae
Origin
The Americas; introduced in Europe (including Wales) and Japan
Water
freshwater

Care

Girardia tigrina, formerly Dugesia tigrina, is a freshwater planarian flatworm and a common pest in shrimp and nano tanks. It should not be sold as livestock. It is native to the Americas but has spread to Europe and Japan; in Britain it is established in Wales, where it has displaced native flatworms. How it arrives: as tiny worms or egg capsules on plants, moss, wood and rock, in live foods, and in water or substrate from other tanks. How to identify it: a flat, soft, brown to grey worm about 1 cm long, with a triangular, arrow-shaped head with two short 'ear' flaps (auricles) and two eyes that look cross-eyed; the back is speckled with dark pigment. It glides smoothly over glass and rock without wriggling. Harmless detritus worms (thin, white, wriggling roundworms or segmented worms) are often mistaken for planaria; detritus worms do no harm. Harm done: it is a predator that eats small invertebrates, including snails, worms and insect larvae, and in aquaria it attacks shrimp eggs, baby shrimp and moulting or weak adults. Large numbers usually mean overfeeding. Removal and prevention: quarantine and rinse new plants and moss; feed less and remove leftovers; use planaria traps baited with meat; remove worms by hand. Fish such as some gouramis and other small fish eat them, but are not suitable for breeding-shrimp tanks. Anti-worm treatments sold for shrimp tanks (such as fenbendazole-based or betel-nut-based products) kill planaria but can also kill snails, so remove snails first and follow the instructions. Dying worms should be removed and followed by a water change. Copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most invertebrates; do not use copper as a planaria treatment in an invertebrate tank. Sources: Wikipedia (en.wikipedia.org/wiki/Girardiatigrina). Checked October 2026.

Diet

A carnivore. In the wild it preys on worms, small crustaceans such as isopods, midge larvae, snails, caddis and mayfly larvae. In aquaria it eats leftover meaty food and attacks shrimp eggs, shrimplets and small snails.

Breeding

Our sources do not cover its reproduction. Planarians in general can reproduce by splitting and regrow from small fragments, as well as laying egg capsules, so cutting or crushing them in the tank does not remove them. Diploid and triploid forms of this species exist.

Compatibility and tank mates

Harmful in shrimp and snail breeding tanks. Harmless to most fish, many of which eat it.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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